1. Field of the Invention
The present invention relates to a novel emulsion type defoaming agent composition effective for the prevention of foaming in an aqueous system, particularly in a strongly alkaline aqueous system.
2. Description of the Prior Art
Foaming in aqueous systems causes various kinds of problems in production processes in various industries, such as a decrease productivity, an increase of defect products, a decrease in the packing ratio of products and the like. Particularly in the industry of pulp production, large amounts of foam producing substances are contained in the waste water and the foaming thereof is the important problem that must be overcome.
In the current method of production of pulp, the Kraft process which is a kind of the alkali process has replaced of the sulfite process which used to be the major process of the industry and the Kraft process is currently the major process.
In the Kraft pulp process, the pulp material (material wood chips) is cooked under pressure in a mixed solution of sodium hydroxide and sodium sulfide and the parts other than the fiber in the wood are removed by dissolving in the solution to obtain the product pulp. In the waste water from the digestion which is generally called the black solution, large amounts of sodium salts of the lignin components and other resin components are contained.
Because these substances have foam forming activity foaming occurs during the separation of these substances from the pulp to cause problems in the production process. The black solution remains in the separated pulp and foaming is again a problem in the pulp washing process.
As described in the above, the foaming which occurs process of washing and screening of pulp after the digestion of the pulp decreases of the efficiency of the washing and the operability of the process to a great extent. The foaming which occurs in the paper making process causes various problems, such as a decrease of strength of the produced paper, decrease in the of quality of the produced paper by formation of spots on the paper, breaks in the paper on the paper machine and the like problems.
Therefore, application of a defoaming agent is indispensable in the production of the pulp.
Various kinds of defoaming agents have been proposed. For example, a defoaming composition comprising 1 to 20 weight % of an aliphatic amide, 1 to 15 weight % of an organic polymer soluble in oil, 1 to 50 weight % of a hydrocarbon oil and 0 to 5 weight % of a fat is described in Japanese Patent Publication 1972-7359 and a defoaming composition comprising 70 to 90 weight % of a non-polar organic fluid, 1 to 5 weight % of a hydrophobic silica and 1 to 20 weight % of an organic phosphorus compound is described in Japanese Patent Publication 1977-5686.
An emulsion comprising 0.5 to 10 weight % of a rapidly cooled amide, 0.3 to 10 weight % of a hydrophobic silica, 0.5 to 5 weight % of a polymer, 0.5 to 5 weight % of an emulsifier, 15 to 65 weight % of an oil, 20 to 60 weight % of water, 0 to 3 weight % of a silicone surface active agent, 0 to 0.5 weight % of a solution of formaldehyde and 0 to 0.5 weight % of a silicone oil is reported in the U.S. Pat. No. 4,225,456.
However, these defoaming agent compositions so far reported do not always exhibit satisfactory defoaming activity. Most of the defoaming agents utilized in the process of Kraft production are insoluble in water. When a defoaming agent of this kind is utilized in a large amount, the defoaming agent coagulates by itself and causes undesirable problems, such as formation of pitch, and environmental problems like contamination of waste water with oil and formation of dioxine.